Apparatus for and method of motor cooling



P 1968 J. w. ENDRES'S 3,402,563

APPARATUS FOR AND METHOD OF MOTOR COOLING Filed Feb. 2, 1967 5 e o 0 on o 0 0 0 0 0 9 23 o o 7 0 0 0 0 0 2 o o o o o o o o o o o o A 27 4 l3 o o o o o o 0 O 0 F o o o o o B O O O 0 0 0 0 0 0 0 4e 42 o o o o o o o o o o INVENTOR.

JAMES W, ENDRESS.

ATTORNEY.

United States Patent 7 ABSTRACT OF THE DISCLOSURE A;refrigeration compressor motor cooling circuit having a metering valve with a fixed orifice therein to restrict refrigerant flow to the motor when there is a large pressure drop across the machine and a-variable orifice in parallel with the fixed orifice operable in response to the pressure variations in the machine to supplement the refrigerant flow through the motor cooling circuit when there is a small pressure drop across the machine.

Background of the invention This invention pertains to refrigeration machines employing refrigerant cooled compressor motors.

In large tonnage refrigerant machines, it is known to utilize liquid refrigerant as a coolant to maintain the compressor motor temperature at a safe level. Liquid refrigerant from the high pressure side of the machine is provided to the motor, where it absorbs the heat produced thereby and is partially vaporized. The liquid and gaseous refrigerant from the motor is vented to a portion of the machine which is at a pressure lower than high side pressure. The most economical and trouble-free way to circulate refrigerant through the motor cooling circuit is by relying on the pressure drop across the machine to force refrigerant therethrough.

While this is satisfactory under normal operating conditions, it should be realized that due to refrigeration machine temperature variations, the pressure drop across the machine and therefore the pressure drop across the motor cooling circuit will vary. For this reason, the cooling circuit is usually sized to provide adequate flow therethrough under normal operating conditions. However, a problem is encountered with a system of this type when the pressure difference between high and low sides of the refrigeration machine decreases. The pressure difference is insufficient to maintain the required liquid refrigerant flow to the motor, causing overheating thereof.

Summary of the invention This invention is directed to a refrigeration machine motor cooling circuit which is capable of providing the proper flow of refrigerant to the compressor motor over a wide range of operating conditions. Under normal operating conditions, a fixed orifice in the motor cooling circuit is employed to limit refrigerant flow therethrough. By relying solely on a fixed orifice for the majority of machine operating conditions encountered, machine reliability is enhanced. Under low head conditions, when the pressure drop across the orifice would be too low to force sufficient refrigerant through the circuit, a supplemental flow is provided by means of a variable orifice valve, responsive to the pressure drop across the machine to pass the required refrigerant through the circuit. Since the variable orifice valve is inoperative a majoirty of the machine Patented Sept. 24, 1968 operating time, the movable parts thereof are not subjected to appreciable wear.

Brief description of the drawings The drawing is a schematic view of a refrigeration machine with a sectional view of a valve mechanism incorporating the refrigerant flow control means of my improved motor cooling refrigerant circuit.

Description of the preferred embodiment Referring more particularly to the drawing, there is shown a refrigeration machine having an evaporator 3, a condenser 5, a refrigerant compressor 7, and a compressor motor 9. A plurality of tubes, hereinafter referred to as tube bundle 4, is disposed in the evaporator for passage therethrough of the medium to be cooled. A tube bundle 6 is disposed in condenser 5 for passage therethrough of cooling water from a suitable source such as a cooling tower (not shown). A float valve 11 is provided in float chamber 13 to regulate the flow of liquid refrigerant from the condenser to the evaporator.

Compressor motor 9 is provided with liquid refrigerant for cooling purposes thereof through motor cooling circuit 15. Liquid refrigerant from float chamber 13 is conveyed through line 17, subcooling loop 19 arranged in evaporator 3, refrigerant flow control valve 21, supply line 22 and refrigerant spray nozzles 23 to motor 9. A vent line 25 is provided to drain refrigerant from the motor to the evaporator. A valve 27 in vent line 25, responsive to the refrigerant pressure in vent line 25 maintains the motor at a slightly higher pressure than the evaporator to minimize lubricant migration from the compressor lubricant system into the motor housing.

It should be understood that the motor pressure is basically low side pressure, the difference between evaporator pressure and motor pressure being approximately one half pound per square inch. It is desirable to keep this pressure difference as low as possible to obtain the greatest possible pressure diiference between the motor housing and compressor to prevent the entrance of compressor lubricant into the motor housing.

The motor cooling circuit flow control valve 21 has a housing 29 with an inlet 31 communicating with refrigerant subcooler loop 19 and an outlet 33 communieating with motor refrigerant supply line 22. A fixed orifice 35 communicating between inlet 31 and outlet 33 allows sufficient refrigerant to flow through the circuit to provide adequate motor cooling under normal operation conditions. A second orifice 37 communicating between inlet 31 and outlet 33 is provided to supplement the refrigerant flow through orifice 35 under low head conditions. Refrigerant flow through orifice 37 is regulated by valve stem 39 which is biased toward open position by spring 41 and toward closed position by condenser pressure acting against side 42 of diaphragm 43. A line 45 provides communication between the condenser and chamber 46 in valve housing 29. Side 44 of diaphragm 43 is subjected to a pressure lower than condenser pressure by means of bleed passage 47 in valve housing 29.

Under normal operating conditions, the pressure drop across the machine is sufficient to hold orifice 37 closed and to provide an adequate flow of refrigerant through orifice 35 for motor cooling purposes. At times, when the pressure drop across the machine is small, such as at start-up, spring 41 in conjunction with low side refrigerant pressure acting on side 44 of diaphragm 43 will counteract the force exerted against side 42 of diaphragm by high side pressure to move the valve stem and open orifice 37 to increase refrigerant flow through the circuit. It can be seen that valve stem 39 will assume an infinite number of positions to vary the flow through orifice 37 under varying low head conditions.

While I have described a preferred embodiment of my invention, it is to be understood that the invention is not limited thereto but may be otherwise embodied within the scope of the following claims.

I claim:

1. A method of cooling the compressor motor in a refrigeration machine comprising the steps of:

providing two liquid refrigerant flow paths in parallel between the motor and the high pressure side of the machine;

venting the motor to the low pressure side of the machine;

restricting the fiow of refrigerant through one of said flow paths to supply sufficient refrigerant to the motor to provide all of the cooling therefor under normal operating conditions; and

regulating the flow of refrigerant through the other of said fiow paths in response to the pressure differential across the machine under low head conditions.

2. A compressor motor cooling circuit for use in a refrigeration machine comprising:

a refrigerant supply line communicating between the high pressure side of the machine and the motor to provide liquid refrigerant thereto;

a refrigerant vent line communicating between the motor and a portion of the machine having a pressure lower than high side pressure for venting refrigerant from the motor;

a first restriction means disposed in said supply line to regulate flow therethrough under normal operating conditions; and, a second restriction means disposed in said supply lines operable in response to low head conditions to supplement the flow of refrigerant to the motor through said first restriction means.

3. A motor cooling circuit according to claim 2 wherein Cir 4 said first restriction means comprises a fixed orifice for passing sufiicient refrigerant to cool the motor under normal operating conditions; and said second restriction means comprises a variable orifice, operable in response to the pressure differential across the machine under low head conditions to supplement the flow of refrigerant through said fixed orifice.

4. A motor cooling circuit according to claim 2 wherein said first and second restriction means are combined in a single valve comprising:

a valve housing having an inlet and an outlet formed therein, the inlet communicating with the low pressure side of the machine and the outlet communicating with the refrigerant compressor motor, said first restriction means comprising a fixed orifice in said valve housing between the inlet and outlet thereof, and second restriction means comprising a variable orifice between the inlet and outlet of said housing, a valve stem operably associated with said variable orifice for regulating the flow of refrigerant therethrough;

biasing means operably associated with said valve stem for urging said valve stem in a direction to maximize the flow through said variable orifice; and

a diaphragm disposed in said valve housing operably associated with said valve stem, the portion of said valve housing on one side of said diaphragm communicating with the high pressure side of the machine to urge said valve stem against said biasing means, the portion of said valve housing on the other side of said diaphragm communicating with the low pressure side of the refrigeration machine.

References Cited UNITED STATES PATENTS MEYER PERLIN, Primary Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, D.C. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,402 ,563 September 24 1968 James W. Endress It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 25, "refrigerant" should read refrigerati line 45, after "between" insert the Column 2, line 33, "lubricant" should read lubrication line 39, after "pressure" insert drop across the motor cooling circuit while providing a sufficient pressure Column 4, line 17, "and" should read said Signed and sealed this 10th day of February 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

